patch 8.2.0426: some errors were not tested for

Problem:    Some errors were not tested for.
Solution:   Add tests. (Dominique Pelle, closes #5824)
diff --git a/src/testdir/test_tcl.vim b/src/testdir/test_tcl.vim
index c2fd191..d25c7f1 100644
--- a/src/testdir/test_tcl.vim
+++ b/src/testdir/test_tcl.vim
@@ -653,6 +653,9 @@
 
 " Test exiting current Tcl interpreter and re-creating one.
 func Test_tcl_exit()
+  call assert_fails('tcl exit 1 1', 'wrong # args: should be "exit ?returnCode?"')
+  call assert_fails('tcl exit x', 'expected integer but got "x"')
+
   tcl set foo "foo"
   call assert_fails('tcl exit 3', 'E572: exit code 3')